Web heater for vacuum packaging machine



Jan. 14, 1964 w. E. mum 3,118,041

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/ IIIIIIIIIIII.' MILL/4N rray/vars United States Patent 3,118,041 WEBHEATER FGR VACUUM PACKAGING MAtCHiNE William E. Young, Believiiie, N1,assignor to Standard Packaging Corporation, New York, N.Y., acorporation of Virginia Filed Mar. 6, 1959, Ser. No. 797,805 Claims.(Cl. 219-19) The present invention relates generally to electricalheaters for plasticizing web material, and more particularly to a heateradapted to operate in conjunction with a vacuum packaging machine inwhich thermoplastic web material is plasticized and vacuum-formed intocontainers for packaging food and other products.

Vacuum packaging machines are known which make use of rolled webs ofthermoplastic film such as Saran, Polyethylene and Mylar. The materialis formed into containers enveloping the commodity being packaged, thecontainers being evacuated and heat sealed. In one such machine, whichis disclosed in the copending application of Mahafiy et al., Serial No.653,084, filed April 16, 1957, (now Patent No. 2,935,828) for ContinuousVacuum Packaging Machine, the web is fed over a rotary drum having moldcavities formed therein. The moving web is first plasticized by a heaterunit such that by applying suction to each cavity, the web material isdrawn therein to form a pocket conforming to the shape of the mold.

In order efiectively to plasticize the web material so as to formpockets of good quality, it is important that the heat be uniformlydistributed throughout the surface of the web. Otherwise wheredifferential heating occurs there is a tendency for the material to thinout in localized areas which are overheated. The various defects whichare encountered as a result of poor web heating are known in the tradeas poor draw, blow outs and popping, these terms being descriptive ofthe nature of the defect.

Another problem which arises in the web heater is in connection withfilm webs having printed matter thereon which may be colored. Theprinted areas tend to absorb more heat radiation than the clear regions,and if the re sultant heat intensity is excessive, the film may burnthrough. For example, blue printing absorbs heat at a much greater ratethan unprinted areas.

Still another problem commonly encountered relates to residual heat inthe web heater. It is customary to provide the web heater with areflector on the side of the lamps away from the film surface, thereflector concentrating the infra energy in the direction of the film.When the machine and the lamps are turned off, the residual heat in thelamps and the reflector may be sufficient to burn the film, therebywasting packaging material.

Another drawback of conventional heaters is that the physicalarrangement of heating elements is such as to produce hot spots inlocalized areas, particularly when the lamps are placed in anintersecting grid pattern. It is found that an excessive heatconcentration occurs at the points of intersection.

In view of the foregoing, it is the principal object of this inventionto provide an improved web heater adapted to plasticize a moving web ofthermoplastic material, the heat being applied uniformly across thesurface of the web such that the temperature thereon is equalized duringthe film forming operation.

More specifically, it is an object of the invention to provide a webheat in which the lamps are all arranged in staggered relationtransversely relative to the direction of film travel, whereby an evenlydiffused heating action is produced to uniformly plasticize the web.

Another object of the invention is to provide a heater element includinga water-cooled reflector of improved r. CC

design which acts quickly to remove residual heat when the lamps areturned off.

Yet another object of the invention is to provide a circuit arrangementfor any array of heater lamps as above described, which circuit isadapted temporarily to boost the voltage through the lamps to permitrapid warm-up of the lamps and thereby reduce waste of packagingmaterial when the machine is started.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the following detaileddescription to be read in conjunction with the accompanying drawings,wherein like components in the various views are identified by likereference numerals.

In the drawings:

FIG. 1 is a perspective view of a vacuum packaging machine whichincludes a web heater in accordance with the invention.

FIG. 2. is a plan view of the web heater unit, per se.

FIG. 3 is a transverse section taken through lines 33 in FIG. 2.

FIG. 4 is an end view of the heater unit looking in the direction ofarrows 4-4 in FIG. 2.

FIG. 5 is a side view of the unit looking in the direction of arrows 55in FIG. 2.

FIG. 6 is a plan view of the reflector incorporated in the heater unit.

FIG. 7 is a side view of the reflector before it is curved into shape.

FiG. 8 shows the curved reflector.

FIG. 9 is a section taken through lines 9-9 in FIG. 6.

FIG. 10 is a schematic diagram of the electrical circuit for operatingthe heater unit elements.

Referring now to FIGS. 1 and 2, the vacuum packaging machine whichincorporates the web heater in accordance with the invention is providedwith a feeding conveyor 10 on which are placed the products 11 to bepackaged. These products may be of any type which benefits from vacuumpackaging, such as sliced luncheon meats, cheese and other perishables.Most bacteria which cause food discoloration and deterioration arenourished by oxygen. When oxygen is removed, bacterial growth isinhibited and the color and flavor 0f the food are retained for a longperiod.

The products 11 in slab form are arranged in double rows on the conveyor10. At the other end of the machine opposite to the conveyor there ismounted a roll of thermoplastic web material 12 which is fed onto avacuum forming drum 13 having a double row of circumferentially arrangedmold cavities 14. The drum acts to form the web into double rows ofpockets surrounded by flange portions. At the input end of the machinethere is mounted a roll of web material 15, this roll having a widthpermitting it to be superimposed over the flanges of the vacuum formedpockets so as to define an enclosure, the interfaces of the webs fromrolls 12 and 15 being heat scalable in character.

The web 15 feeds upwardly to the exit end of the conveyor in where theproducts are transferred to the web, the latter then travellingdownwardly over a supporting structure 16 to the lower portion of thedrum 13 where the vacuum formed pockets, now inverted, are fitted overthe products. The superimposed webs with the products enclosed betweenthem are next sealed together around the peripheries of the pockets,excepting for small passageway areas, by a heat sealing unit at thelower end of the drum. The now partly completed packages continue underthe drum '13 to an evacuating and final heatsealing head. If desired,the packages may be gassed while in the final head subsequent to theevacuation and prior to the heat-sealing. Appropriately arranged knives3 sever the packages to form individual packages which fall down a chute17 to an output conveyor 18.

The web heater unit, generally designated by numeral 19, is mountedabove the drum 13 against the control panel 29, the unit having anarcuate shape conforming to the curvature of the drum. The web materialfrom roll 12 is carried over the cavities lid in drum 13 and passesunder the heater unit 19. A vacuum system communicating with thecavities is so operated that when the web material is plasticized by theheater, the suction is made operative to draw the softened material intothe cavities.

The general arrangement of drum and heater as well as the other machinecomponents is disclosed in the abovementioned copending application. Thepresent invention is concerned only with the structure and operation ofthe heater unit and will now be described in connection with FIGS. 2 to10.

Referring now to FIGS. 2 to 5, the heat unit is con stituted by arectangular metal frame constituted by two trapezoidal side plates 21and 22 and two angle bars 23 and 24. Mounted against the side plates 21and 22; are two channel members 25 and Secured by brackets to the endsof the channel members are arch-sha ed insulating mounts 2'7 and 23 ofTeflon or similar dielectric material, the mounts lying in spacedparallel relation to the end pieces 23 and 2 2. Attached to the endpieces are arch-shaped insulators 29 and 3% which dimensionally matchthe insulation mounts. The heater is mounted in position over the drumby means including brackets 31 and 32.

As best seen in 1G. 3, the mounts 27 and 28 are each formed with aseries of equi-spaced radial slots a, b, c, a, e, etc., for receivingthe terminal pins of heat lamps. Seventeen heater lamps L to 1 areprovided, the slots being alternately long and short in length wherebywhen the lamp pins are inserted, the lamps are caused to occupystaggered positions.

The lamps L to L all extend transversely relative to the direction offilm movement, as best seen in FIG. 2. The lamps act as infra-redradiators comprising transparent tubes enclosing resistance elementsterminating in connecting pins P and P which are received in the slotsof the mount.

In practice the elements may each have a 500 watt rating. The distancebetween slots is smaller than the diameter of the lamps but because ofthe staggered arrangement it becomes possible to crowd the seventeenlamps within a relatively small are such that radiation is producedthroughout the area without the existence of open or non-radiatingspaces between the lamps. The pins P and P extend into the insulatedspace between the mounts 27 and 28 and the insulators and 3b, and arethereby isolated from the metal frame. Connecting leads are attached tothe pins for applying voltage thereto.

The water-cooled reflector 33 is generally rectangular in form and iscurved to rest on top of the mounts. The reflector, as best seen inF168. 6 and 7, is preferably made of two sheets of aluminum and 3322 bythe roll bond method in which a silk screen pattern is laid outsinuously in the path of the water passageway 33c on the two sheets. Thepassageway is coated with a substance which prevents bonding, such thatwhen the two sheets are rolled and bonded together as one piece, fusionoccurs only in the non-coated areas. Pressure is then applied to theunbonded passageways and this serves to open up the duct area 330, asbest seen in FIG. 9. Input and output pipes 34 and 35 are connected tothe ends of the water passageway. The reflector, which is initially infiat form as shown in FIG. 7, is curved to shape as shown in FIG. 8.

It will be seen in FIG. 2 that when the reflector is in position overthe lamps, the parallel main passages therein are perpendicular to thelamps for most effective cooling. The fiow of water in the reflectorremoves heat quickly therefrom, this flow being maintained even afterthe lamps are turned off to dissipate any residual heat from the lampsand the reflector.

Referring now to FIG. 10, the electrical circuit for the lamps L to L isshown, the voltage source being a three-phase line 1 I and 1 which isconnected through a suitable switch 36 to a three-phase voltage controlvariac 37 having three adjustable impedance branches and slidingcontacts 38, 39 and 4t? therefor.

The lamps L to L are connected in an unbalanced delta circuit. Lamps Lto L, are serially connected as a string in one branch of the delta,lamps L to L are serially connected in another branch, and lamps L to Lare serially connected in the third branch. Shunted across the lamps Lto L in the third branch are the serially-connected lamps L to LTherefore each series string consists of four lamps except for thestring of lamps L13 to L17.

Sliding contact of the variac is connected to junction 1 in the delta,contact 39 to junction 1 and contact 4% to junction 3 Thus tie samemagnitude of voltis applied across each string of lamps in the delta andone-fourth of this voltage appears across each lamp in the seriesstring, save for the five lamp string L to L where only one-fifth of thetotal voltage is developed across the lamps therein.

Consequently since the lamps L and L are arrayed one after the other instaggered relation in the direction of film travel, the lamps L to L areuniformly heated, whereas the remaining lamps L to L are all heated to arelatively lower temperature. This is desirable in order to reduce thetemperature somewhat on the exit side of the heater unit.

In order to reduce waste of packaging material when the packagingmachine is started, circuit means are provided to permit rapid warm-upof the heater lamps. This is accomplished by a manually-operated boosterswitch '41 which is arranged to connect variac contact 40 to themidpoint of series string L to L variac contact 39 to the midpoint ofseries string L to L and variac contact 38 to the midpoint of string Lto L In addition, variac contact 38 is connected between lamps L and Lin the five lamps string L to L This booster action doubles the voltageacross all lamps, with the exception of lamps L to L where the increaseis not quite as great. Since the lamps are operated above their ratedvalue when the booster switch 41 is turned on, this causes a rapidwarm-up and as soon as the desired temperature is reached, the switch 41is cut oil and the lamps revert to their normal operating voltage.

While there has been shown what is considered to be a preferredembodiment of the invention, it will be manifest that many changes andmodifications may be made therein Without departing from the essentialspirit of the invention. It is intended, therefore, in the annexedclaims to cover all such changes and modifications as fall within thetrue scope of the invention.

What is claimed is:

1. A web heater unit adapted to plasticizc a web of film travelling on avacuum molding drum, said heater unit comprising an arcuate array oftubular heater lamps disposed in alternately staggered relation over thedrum transversely relative to the filmmovement to provide uniformlydiffused radiation of heat, means electrically to energize said lamps atgiven voltages for normal operation, and switch means momentarily toboost said voltages to effect rapid warm-up of said heater unit.

2. A web heater unit adapted to plasticize a web of film travelling on avacuum molding drum, said heater unit comprising an arcuate array oftubular resistance heater lamps disposed in alternately staggeredrelation over the drum transversely relative to the film movement toprovide uniformly dilfused radiation of heat, and means electrically toenergize all lamps in said array with the same voltage, except for thelamps in the end portion of the array at the exit side of the film, saidend portion lamps being energized at a lower voltage.

3. A web heater unit, as set forth in claim 2, further including boostermeans temporarily to increase the voltages across said lamps to effectrapid warm-up thereof.

4. A web heater unit adapted to plasticize a web of film travelling on avacuum molding drum, said heater unit comprising a rectangular framesupportable over said drum, a pair of arch-shaped insulating mountsmounted within said frame adjacent the ends thereof and having radialslots formed therein at equi-spaced positions, said slots beingalternately short and long, a plurality of tubular resistance heatingelements supported between said mounts transversely relative to thedirection of film movement and having terminal pins receivable incorresponding slots in said mounts whereby said elements are arrayed instaggered relation over said drum.

5. A heater unit, as set forth in claim 4, wherein the distance betweenradial slots is smaller than the diameter of said tubular elements.

6. A web heater unit adapted to plasticize a web of film travelling on avacuum molding drum, said heater unit comprising a rectangular framesupportable over said drum, a pair of arch-shaped insulating mountsmounted within said frame adjacent the ends thereof and having radialslots formed therein at equispaced positions, said slots beingalternately short and long, a plurality of tubular heating elementssupported between said mounts transversely relative to the direction offilm movement and having terminal pins receivable in corresponding slotsin said mounts whereby said elements are arrayed in staggered relationover said drum, and a curved watercooled reflector supported on saidmounts above said lamps.

7. A web heater unit adapted to plasticize a web of film travelling on avacuum molding drum, said heater unit comprising a rectangular framesupportable over said drum, a pair of arch-shaped insulating mountsmounted within said frame adjacent the ends thereof and having radialslots formed therein at spaced positions, said slots being alternatelyshort and long, a plurality of tubular heating elements supportedbetween said mounts transversely relative to the direction of movementand having terminal pins receivable in corresponding slots in saidmounts whereby said elements are arrayed in staggered relation over saiddrum, and means selectively to energize said lamps with voltagesproducing normal heating and relatively large booster voltages effectingrapid warm-up.

8. A web heater unit adapted to plasticize a web of film travelling on avacuum molding drum, said heater unit comprising a rectangular framesupportable over said drum, a pair of arch-shaped insulating mountsmounted within said frame adjacent the ends thereof and having radialslots formed therein at spaced positions, said slots being alternatelyshort and long, a plurality of tubular heating elements supportedbetween said movements transversely relative to the direction of filmmovement and having terminal pins receivable in corresponding slots insaid mounts whereby said elements are arrayed in staggered relation oversaid drum, and a curved watercooled reflector supported on said mountsabove said lamps, said reflector including a sinuous water passagewayproviding parallel paths extending perpendicularly relative to saidlamps.

9. A web heater unit, as set forth in claim 6, further including athree-phase circuit for energizing said lamps comprising a delta eachbranch of which includes a like given number of serially-connectedlamps, and an additional string of series connected lamps connected inshunt relation across one of said branches and provided with a greaternumber of lamps than said given number, and means to connect athree-phase source to the junctions of said delta whereby all lamps areheated to the same degree except those in said additional string.

10. A web heater unit, as set forth in claim 9, further includingbooster switch means connected to an intermediate point in each stringof lamps in said delta to increase the operating voltage thereofmomentarily.

References Cited in the file of this patent UNITED STATES PATENTS1,492,595 Edmands May 6, 1924 1,646,010 Clover Oct. 18, 1927 1,896,398Gay Feb. 7, 1933 1,960,697 Cochran et a1 May 29, 1934 2,028,453 HoffmanJan. 21, 1936 2,3 69,803 Sardeson Feb. 2 0, 1945 2,561,092 Bell July'17, 19:51 2,655,802 Ravich Oct. 20, 1953 2,956,149 Dowell et al Oct.11, 1960 3,008,029 Davis et al. Nov. 7, 1961 FOREIGN PATENTS 795,921France Jan. 13, 1936 180,573 Austria Dec. 27, 1954

1. A WEB HEATER UNIT ADAPTED TO PLASTICIZE A WEB OF FILM TRAVELING ON AVACUUM MOLDING DRUM, SAID HEATER UNIT COMPRISING AN ARCUATE ARAY OFTUBULAR HEATER LAMPS DISPOSED IN ALTERNATELY STAGGERED RELATION OVER THEDRUM TRANSVERSELY RELATIVE TO THE FILM MOVEMENT TO PROVIDE UNIFORMLYDIFFUSED RADIATION OF HEAT, MEANS ELECTRICLLY TO ENERGIZE SAID LAMPS ATGIVEN VOLTGAGES FOR NORMAL OPERATION, AND SWITCH MEANS MOMENTARILY TOBOOST AND VOLTAGES TO EFFECT RAPID WARM-UP OF SAID HEATER UNIT.